Russell Is this series something you would be willing to pull into your tree? Daniel On Tue, 2010-09-07 at 11:23 -0700, Stephen Boyd wrote: > (Sorry, resending due to stray comma...) > > These patches are another attempt at fixing the udelay() > issue pointed out on arm-lkml[1][2]. A quick recap: some SMP > machines can scale their CPU frequencies independent of one > another. loops_per_jiffy is calibrated globally and used in > __const_udelay(). If one CPU is running faster than what the > loops_per_jiffy is calculated (or scaled) for, udelay() will > be incorrect and not wait long enough (or too long). A similar > problem occurs if the cpu frequency is scaled during a udelay() > call. > > We could fix this issue a couple ways, wholesale replacement > of __udelay() and __const_udelay() (see [2] for that approach), > or replacement of __delay() (this series). Option 1 can fail if > anybody uses udelay() before memory is mapped and also duplicates > most of the code in asm/delay.h. It also needs to hardcode the > timer tick frequency, which can sometimes be inaccurate. The > benefit is that loops_per_jiffy stays the same and thus BogoMIPS > is unchanged. Option 2 can't fail since the __delay() loop is > replaced after memory is mapped in, but it suffers from a low > BogoMIPS when timers are clocked slowly. It also more accurately > calculates the timer tick frequency through the use of > calibrate_delay_direct(). > > -- Reference -- > [1] http://article.gmane.org/gmane.linux.kernel/977567 > [2] http://article.gmane.org/gmane.linux.ports.arm.kernel/78496 > > Stephen Boyd (3): > [ARM] Translate delay.S into (mostly) C > [ARM] Allow machines to override __delay() > [ARM] Implement a timer based __delay() loop > > arch/arm/include/asm/delay.h | 5 ++- > arch/arm/kernel/armksyms.c | 4 -- > arch/arm/lib/delay.S | 65 ------------------------------ > arch/arm/lib/delay.c | 90 ++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 94 insertions(+), 70 deletions(-) > delete mode 100644 arch/arm/lib/delay.S > create mode 100644 arch/arm/lib/delay.c > -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
